Chapter 1 Introduction to Computers, Programs, and Java

Chapter 1 Introduction to Computers, Programs, and Java 1

Objectives To understand computer basics, programs, and operating systems ( 1.2 1.4). To describe the relationship between Java and the World Wide Web ( 1.5). To understand the meaning of Java language specification, API, JDK, and IDE ( 1.6). To write a simple Java program ( 1.7). To display output on the console ( 1.7). To explain the basic syntax of a Java program ( 1.7). To create, compile, and run Java programs ( 1.8). To display output using the JOptionPane message dialog boxes ( 1.9). To become familiar with Java programming style and documentation ( 1.10). To explain the differences between syntax errors, runtime errors, and logic errors ( 1.11). 2

What is a Computer? A computer consists of a CPU, memory, hard disk, floppy disk, monitor, printer, and communication devices. Bus Storage Devices Memory CPU Communication Devices Input Devices Output Devices e.g., Disk, CD, and Tape e.g., Modem, and NIC e.g., Keyboard, Mouse e.g., Monitor, Printer 3

CPU The central processing unit (CPU) is the brain of a computer. It retrieves instructions from memory and executes them. The CPU speed is measured in megahertz (MHz), with 1 megahertz equaling 1 million pulses per second. The speed of the CPU has been improved continuously. If you buy a PC now, you can get an Intel Pentium 4 Processor at 3 gigahertz (1 gigahertz is 1000 megahertz). Bus Storage Devices Memory CPU Communication Devices Input Devices Output Devices e.g., Disk, CD, and Tape e.g., Modem, and NIC e.g., Keyboard, Mouse e.g., Monitor, Printer 4

Memory Memory is to store data and program instructions for CPU to execute. A memory unit is an ordered sequence of bytes, each holds eight bits. A program and its data must be brought to memory before they can be executed. A memory byte is never empty, but its initial content may be meaningless to your program. The current content of a memory byte is lost whenever new information is placed in it. Bus Storage Devices Memory CPU Communication Devices Input Devices Output Devices e.g., Disk, CD, and Tape e.g., Modem, and NIC e.g., Keyboard, Mouse e.g., Monitor, Printer 5

How Data is Stored? Data of various kinds, such as numbers, characters, and strings, are encoded as a series of bits (zeros and ones). Computers use zeros and ones because digital devices have two stable states, which are referred to as zero and one by convention. The programmers need not to be concerned about the encoding and decoding of data, which is performed automatically by the system based on the encoding scheme. The encoding scheme varies. For example, character J is represented by 01001010 in one byte. A small number such as three can be stored in a single byte. If computer needs to store a large number that cannot fit into a single byte, it uses a number of adjacent bytes. No two data can share or split a same byte. A byte is the minimum storage unit. Memory address... 2000 2001 2002 2003 2004 Memory content... 01001010 Encoding for character J 01100001 Encoding for character a 01110110 Encoding for character v 01100001 Encoding for character a 00000011 Encoding for number 3 6

Storage Devices Memory is volatile, because information is lost when the power is off. Programs and data are permanently stored on storage devices and are moved to memory when the computer actually uses them. There are three main types of storage devices:disk drives (hard disks and floppy disks), CD drives (CD-R and CD-RW), and Tape drives. Bus Storage Devices Memory CPU Communication Devices Input Devices Output Devices e.g., Disk, CD, and Tape e.g., Modem, and NIC e.g., Keyboard, Mouse e.g., Monitor, Printer 7

Output Devices: Monitor The monitor displays information (text and graphics). The resolution and dot pitch determine the quality of the display. Bus Storage Devices Memory CPU Communication Devices Input Devices Output Devices e.g., Disk, CD, and Tape e.g., Modem, and NIC e.g., Keyboard, Mouse e.g., Monitor, Printer 8

Monitor Resolution and Dot Pitch resolution The screen resolution specifies the number of pixels in horizontal and vertical dimensions of the display device. Pixels (short for picture elements ) are tiny dots that form an image on the screen. A common resolution for a 17-inch screen, for example, is 1,024 pixels wide and 768 pixels high. The resolution can be set manually. The higher the resolution, the sharper and clearer the image is. dot pitch The dot pitch is the amount of space between pixels, measured in millimeters. The smaller the dot pitch, the sharper the display. 9

Communication Devices A regular modem uses a phone line and can transfer data in a speed up to 56,000 bps (bits per second). A DSL (digital subscriber line) also uses a phone line and can transfer data in a speed 20 times faster than a regular modem. A cable modem uses the TV cable line maintained by the cable company. A cable modem is as fast as a DSL. Network interface card (NIC) is a device to connect a computer to a local area network (LAN). The LAN is commonly used in business, universities, and government organizations. A typical type of NIC, called 10BaseT, can transfer data at 10 mbps (million bits per second). Bus Storage Devices Memory CPU Communication Devices Input Devices Output Devices e.g., Disk, CD, and Tape e.g., Modem, and NIC e.g., Keyboard, Mouse e.g., Monitor, Printer 10

Programs Computer programs, known as software, are instructions to the computer. You tell a computer what to do through programs. Without programs, a computer is an empty machine. Computers do not understand human languages, so you need to use computer languages to communicate with them. Programs are written using programming languages. 11

Programming Languages Machine Language Assembly Language High-Level Language Machine language is a set of primitive instructions built into every computer. The instructions are in the form of binary code, so you have to enter binary codes for various instructions. Program with native machine language is a tedious process. Moreover the programs are highly difficult to read and modify. For example, to add two numbers, you might write an instruction in binary like this: 1101101010011010 12

Programming Languages Machine Language Assembly Language High-Level Language Assembly languages were developed to make programming easy. Since the computer cannot understand assembly language, however, a program called assembler is used to convert assembly language programs into machine code. For example, to add two numbers, you might write an instruction in assembly code like this: ADDF3 R1, R2, R3 Assembly Source File Machine Code File ADDF3 R1, R2, R3 Assembler 1101101010011010 13

Programming Languages Machine Language Assembly Language High-Level Language The high-level languages are English-like and easy to learn and program. For example, the following is a high-level language statement that computes the area of a circle with radius 5: area = 5 * 5 * 3.1415; 14

Popular High-Level Languages Language Ada BASIC C C++ C# COBOL FORTRAN Java Pascal Python Visual Basic Description Named for Ada Lovelace, who worked on mechanical general-purpose computers. The Ada language was developed for the Department of Defense and is used mainly in defense projects. Beginner s All-purpose Symbolic Instruction Code. It was designed to be learned and used easily by beginners. Developed at Bell Laboratories. C combines the power of an assembly language with the ease of use and portability of a high-level language. C++ is an object-oriented language, based on C. Pronounced C Sharp. It is a hybrid of Java and C++ and was developed by Microsoft. COmmon Business Oriented Language. Used for business applications. FORmula TRANslation. Popular for scientific and mathematical applications. Developed by Sun Microsystems, now part of Oracle. It is widely used for developing platformindependent Internet applications. Named for Blaise Pascal, who pioneered calculating machines in the seventeenth century. It is a simple, structured, general-purpose language primarily for teaching programming. A simple general-purpose scripting language good for writing short programs. Visual Basic was developed by Microsoft and it enables the programmers to rapidly develop graphical user interfaces. 15

Interpreting/Compiling Source Code A program written in a high-level language is called a source program or source code. Because a computer cannot understand a source program, a source program must be translated into machine code for execution. The translation can be done using another programming tool called an interpreter or a compiler. 16

Interpreting Source Code An interpreter reads one statement from the source code, translates it to the machine code or virtual machine code, and then executes it right away, as shown in the following figure. Note that a statement from the source code may be translated into several machine instructions. High-level Source File area = 5 * 5 * 3.1415;... Interpreter Output 17

Compiling Source Code A compiler translates the entire source code into a machine-code file, and the machine-code file is then executed, as shown in the following figure. High-level Source File Machine-code File area = 5 * 5 * 3.1415;... Compiler 0101100011011100 1111100011000100 Executor Output 18

Operating Systems The operating system (OS) is a program that manages and controls a computer s activities. The popular operating systems for general-purpose computers are Microsoft Windows, Mac OS, and Linux. Application programs, such as a Web browser or a word processor, cannot run unless an operating system is installed and running on the computer. User Application Programs Operating System Hardware 19

Why Java? The answer is that Java enables users to develop and deploy applications on the Internet for servers, desktop computers, and small hand-held devices. The future of computing is being profoundly influenced by the Internet, and Java promises to remain a big part of that future. Java is the Internet programming language. Java is a general purpose programming language. Java is the Internet programming language. 20

Java, Web, and Beyond Java can be used to develop Web applications. Java Applets Java Web Applications Java can also be used to develop applications for hand-held devices such as Palm and cell phones 21

Examples of Java s Versatility (Applets) 22

PDA and Cell Phone 23

Java s History James Gosling and Sun Microsystems Oak Java, May 20, 1995, Sun World HotJava The first Java-enabled Web browser Early History Website: http://www.java.com/en/javahistory/index.jsp 24

Companion Characteristics of Java Website Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Java's Performance Java Is Multithreaded Java Is Dynamic www.cs.armstrong.edu/liang/javacharacteristics.pdf 25

Companion Website Characteristics of Java Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Java's Performance Java Is Multithreaded Java Is Dynamic Java is inherently object-oriented. Although many object-oriented languages began strictly as procedural languages, Java was designed from the start to be object-oriented. Object-oriented programming (OOP) is a popular programming approach that is replacing traditional procedural programming techniques. One of the central issues in software development is how to reuse code. Objectoriented programming provides great flexibility, modularity, clarity, and reusability through encapsulation, inheritance, and polymorphism. 27

Companion Website Characteristics of Java Java Is Simple Java Is Object-Oriented Java Is Distributed Java Is Interpreted Java Is Robust Java Is Secure Java Is Architecture-Neutral Java Is Portable Java's Performance Java Is Multithreaded Java Is Dynamic Java compilers can detect many problems that would first show up at execution time in other languages. Java has eliminated certain types of errorprone programming constructs found in other languages. Java has a runtime exception-handling feature to provide programming support for robustness. 30

JDK 1.02 (1995) JDK 1.1 (1996) JDK 1.2 (1998) JDK 1.3 (2000) JDK 1.4 (2002) JDK Versions JDK 1.5 (2004) a. k. a. JDK 5 or Java 5 JDK 1.6 (2006) a. k. a. JDK 6 or Java 6 JDK 1.7 (2011) a. k. a. JDK 7 or Java 7 37

JDK Editions Java Standard Edition (J2SE) J2SE can be used to develop client-side standalone applications or applets. Java Enterprise Edition (J2EE) J2EE can be used to develop server-side applications such as Java servlets, Java ServerPages, and Java ServerFaces. Java Micro Edition (J2ME). J2ME can be used to develop applications for mobile devices such as cell phones. This book uses J2SE to introduce Java programming. 38

Popular Java IDEs NetBeans Eclipse 39

A Simple Java Program Listing 1.1 //This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); Welcome Run IMPORTANT NOTE: (1) To enable the buttons, you must download the entire slide file slide.zip and unzip the files into a directory (e.g., c:\slide). (2) You must have installed JDK and set JDK s bin directory in your environment path (e.g., c:\program Files\java\jdk1.7.0\bin in your environment path. (3) If you are using Office 2010, check PowerPoint2010.doc located in the same folder with this ppt file. 40

Creating and Editing Using NotePad To use NotePad, type notepad Welcome.java from the DOS prompt. 41

Creating and Editing Using WordPad To use WordPad, type write Welcome.java from the DOS prompt. 42

Creating, Compiling, and Running Programs Create/Modify Source Code Source code (developed by the programmer) public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); Saved on the disk Source Code Byte code (generated by the compiler for JVM to read and interpret, not for you to understand) Method Welcome() 0 aload_0 Method void main(java.lang.string[]) 0 getstatic #2 3 ldc #3 <String "Welcome to Java!"> 5 invokevirtual #4 8 return Compile Source Code i.e., javac Welcome.java stored on the disk Bytecode Run Byteode i.e., java Welcome If compilation errors Result Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 If Pearson runtime errors Education, or incorrect Inc. All result 43

Compiling Java Source Code You can port a source program to any machine with appropriate compilers. The source program must be recompiled, however, because the object program can only run on a specific machine. Nowadays computers are networked to work together. Java was designed to run object programs on any platform. With Java, you write the program once, and compile the source program into a special type of object code, known as bytecode. The bytecode can then run on any computer with a Java Virtual Machine, as shown below. Java Virtual Machine is a software that interprets Java bytecode. Java Bytecode Java Virtual Machine Any Computer 44

animation Trace a Program Execution Enter main method //This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 45

animation Trace a Program Execution Execute statement //This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 46

animation Trace a Program Execution //This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); print a message to the console 47

Two More Simple Examples WelcomeWithThreeMessages Run ComputeExpression Run 48

Companion Website Supplements on the Companion Website See Supplement I.B for installing and configuring JDK See Supplement I.C for compiling and running Java from the command window for details www.cs.armstrong.edu/liang/intro8e 49

Companion Website Compiling and Running Java from the Command Window Set path to JDK bin directory set path=c:\program Files\java\jdk1.6.0\bin Set classpath to include the current directory set classpath=. Compile javac Welcome.java Run java Welcome 50

Compiling and Running Java Companion Website from TextPad See Supplement II.A on the Website for details 51

Companion Website Compiling and Running Java from Eclipse See Supplement II.D on the Website for details 52

Companion Website Compiling and Running Java from NetBeans See Supplement I.D on the Website for details 53

Anatomy of a Java Program Class name Main method Statements Statement terminator Reserved words Comments Blocks 54

Class Name Every Java program must have at least one class. Each class has a name. By convention, class names start with an uppercase letter. In this example, the class name is Welcome. //This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 55

Main Method Line 2 defines the main method. In order to run a class, the class must contain a method named main. The program is executed from the main method. //This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 56

Statement A statement represents an action or a sequence of actions. The statement System.out.println("Welcome to Java!") in the program in Listing 1.1 is a statement to display the greeting "Welcome to Java!. //This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 57

Statement Terminator Every statement in Java ends with a semicolon (;). //This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 58

Reserved words Reserved words or keywords are words that have a specific meaning to the compiler and cannot be used for other purposes in the program. For example, when the compiler sees the word class, it understands that the word after class is the name for the class. //This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 59

Blocks A pair of braces in a program forms a block that groups components of a program. public class Test { public static void main(string[] args) { System.out.println("Welcome to Java!"); Method block Class block 60

Special Symbols Character Name Description { () [] // " " ; Opening and closing braces Opening and closing parentheses Opening and closing brackets Double slashes Opening and closing quotation marks Semicolon Denotes a block to enclose statements. Used with methods. Denotes an array. Precedes a comment line. Enclosing a string (i.e., sequence of characters). Marks the end of a statement. 61

{ // This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 62

( ) // This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 63

; // This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 64

// // This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 65

" " // This program prints Welcome to Java! public class Welcome { public static void main(string[] args) { System.out.println("Welcome to Java!"); 66

Displaying Text in a Message Dialog Box you can use the showmessagedialog method in the JOptionPane class. JOptionPane is one of the many predefined classes in the Java system, which can be reused rather than reinventing the wheel. WelcomeInMessageDialogBox Run IMPORTANT NOTE: (1) To enable the buttons, you must download the entire slide file slide.zip and unzip the files into a directory (e.g., c:\slide). (2) You must have installed JDK and set JDK s bin directory in your environment path (e.g., c:\program Files\java\jdk1.7.0\bin in your environment path. (3) If you are using Office 2010, check PowerPoint2010.doc located in the same folder with this ppt file. 67

The showmessagedialog Method JOptionPane.showMessageDialog(null, "Welcome to Java!", "Display Message", JOptionPane.INFORMATION_MESSAGE); 68

Two Ways to Invoke the Method There are several ways to use the showmessagedialog method. For the time being, all you need to know are two ways to invoke it. One is to use a statement as shown in the example: JOptionPane.showMessageDialog(null, x, y, JOptionPane.INFORMATION_MESSAGE); where x is a string for the text to be displayed, and y is a string for the title of the message dialog box. The other is to use a statement like this: JOptionPane.showMessageDialog(null, x); where x is a string for the text to be displayed. 69

Programming Style and Documentation Appropriate Comments Naming Conventions Proper Indentation and Spacing Lines Block Styles 70

Appropriate Comments Include a summary at the beginning of the program to explain what the program does, its key features, its supporting data structures, and any unique techniques it uses. Include your name, class section, instructor, date, and a brief description at the beginning of the program. 71

Naming Conventions Choose meaningful and descriptive names. Class names: Capitalize the first letter of each word in the name. For example, the class name ComputeExpression. 72

Proper Indentation and Spacing Indentation Indent two spaces. Spacing Use blank line to separate segments of the code. 73

Block Styles Use end-of-line style for braces. Next-line style public class Test { public static void main(string[] args) { System.out.println("Block Styles"); public class Test { public static void main(string[] args) { System.out.println("Block Styles"); End-of-line style 74

Syntax Errors Programming Errors Detected by the compiler Runtime Errors Causes the program to abort Logic Errors Produces incorrect result 75

Syntax Errors public class ShowSyntaxErrors { public static main(string[] args) { System.out.println("Welcome to Java); 76

Runtime Errors public class ShowRuntimeErrors { public static void main(string[] args) { System.out.println(1 / 0); 77

Logic Errors public class ShowLogicErrors { public static void main(string[] args) { System.out.println("Celsius 35 is Fahrenheit degree "); System.out.println((9 / 5) * 35 + 32); 78